What's the sensor size of your camera? Please select… Large Format Film 8x10 Large Format Film 5x7 Large Format Film 4x5 Medium Format Film 6x7 Medium Format Film 6x6 Medium Format Film 6x4.5 Phase One P 65+, IQ160, IQ180 Medium Format (Hasselblad H5D-60) Kodak KAF 39000 CCD Pentax 645D, Hasselblad X1D-50c, CFV-50c, Fuji GFX 50S Leica S Full Frame APS-H (Canon) APS-C (Nikon, Sony, Pentax, Fuji…), Sigma Foveon APS-C (Canon) Original Sigma Foveon X3 Four Thirds, Micro Four Thirds (Olympus, Panasonic) 1" (Sony, Nikon, Samsung) 2/3" (Nokia Lumia 1020, Fujifilm X-S1, X20, XF1) 1/1.7" (Pentax Q7, Canon G10, G15) 1/2.5" 1/3" (iPhone 5s, 6, 7)
If you want the equivalent of a Full Frame mm, you should get a ??mm lens.
A lens with the focal length of mm will behave like a ??mm in Full Frame.
Wanna see how it works with zoom lenses? Instead of a single value, enter the zoom value, e.g.: 18-80
This thing was made to be used. Ratio values based on Wikipedia:Image sensor format. Check the code on GitHub, not my best code but it shipped.